Federal authorities are investigating an act of vandalism at the headquarters of the Islamic Society of North America near Indianapolis as a possible hate crime.

An FBI spokeswoman in Indianapolis on Thursday confirmed a hate-crime investigation has been opened. It's in response to vandals spray-painting vulgar graffiti on an exterior wall of the group's headquarters in Plainfield on Sunday. The graffiti included profanity, racial epithets and references to suicide bombings.

FBI Special Agent Wendy Osborn says the investigation is ongoing. She declined comment on whether authorities might have identified any suspects.

Security camera footage showed three people taking part. But police have said the footage wasn't clear enough to identify suspects.